Multiple sclerosis (MS) is an
autoimmune disease that affects the CNS and it is characterized by
inflammation,
demyelination, remyelination,
gliosis and axonal damage that occur mainly in the spinal cord.
Cannabinoids have been proposed as promising therapeutic agents in MS given their capability to alleviate specific MS symptoms (e.g., spasticity,
pain). Although MS has been considered mainly an inflammatory disorder, recent evidence, however, revealed the importance of neurodegenerative events, opening the possibility that
cannabinoid agonists, given their cytoprotective properties, may also serve to reduce oligodendrocyte death and axonal damage in MS. Thus, the treatment with WIN55,512-2, a potent CB(1) and CB(2) agonist, was reported to be effective to ameliorate
tremor and spasticity in mice with chronic relapsing
experimental autoimmune encephalomyelitis, a murine model of MS, but also to delay
disease progression in this and other murine models of MS. The purpose of this investigation was to further explore the mechanism(s) underlying the amelioration in
disease progression caused by WIN55,212-2. We have particularly focused on anti-glutamatergic and anti-inflammatory effects of this
cannabinoid agonist. In this study, we used mice treated with
myelin oligodendrocyte glycoprotein (MOG) that induces a progressive pattern of EAE and conducted the pharmacological experiments in early stages of the disease. As expected, the administration of WIN55,512-2 (5 mg/kg, i.p) had a positive effect in reducing neurological disability and improving motor coordination of EAE mice. Levels of
glutamate and
GABA in the spinal cord and also in the brainstem of EAE mice were similar to control animals, and, accordingly, they were not altered by the treatment with WIN55,212-2. However, EAE mice showed some subtle alterations in
mRNA levels for the
glutamate transporter GLT1 and, to a lesser extent, GLAST too, changes that were altered by the treatment with WIN55,212-2 in the spinal cord, but not in the brainstem. Regarding to inflammatory responses, EAE mice showed a marked up-regulation in
mRNA levels for COX-2, inducible NOS and TNF-α in the spinal cord and the brainstem, these responses being attenuated after the treatment with WIN55,212-2. We also observed the presence of cell aggregates in the spinal cord of EAE mice that were significantly attenuated by the treatment with WIN55,212-2. Immunohistochemical analysis (with Iba-1 and Cd11b) of these aggregates indicated that they corresponded to microglia (resident macrophages) and peripheral macrophages. Lastly, experiments conducted with selective antagonists for the CB(1) (e.g.
rimonabant) or CB(2) (e.g. AM-630) receptors revealed that WIN55,212-2 effects in EAE mice were mediated by the activation of CB(1) but not CB(2) receptors, as reflected the reversion of positive effects of this
cannabinoid on neurological decline, TNF-α generation and accumulation of cell aggregates in the spinal cord with
rimonabant, but not with
AM-630. This was concordant with the lack of positive effects on neurological decline observed in EAE mice when they received
HU-308, a selective CB(2) receptor agonist, instead WIN55,212-2. In summary, the treatment of EAE mice with the
cannabinoid agonist WIN55,512-2 reduced their neurological disability and the progression of the disease. This effect was exerted through the activation of CB(1) receptors, which would exert a positive influence in the reduction of inflammatory events linked to the pathogenesis of this disease.